Homocystinuria

Definition

Homocystinuria is an inherited disorder that affects the metabolism of the amino acid methionine.

Alternative Names

Cystathionine beta synthase deficiency

Causes, incidence, and risk factors

Homocystinuria is inherited in families as an autosomal recessive trait. This means that the child must inherit the defective gene from both parents to be seriously affected.

Homocystinuria has several features in common with Marfan syndrome. Unlike Marfan syndrome, in which the joints tend to be "loose," in homocysturia the joints tend to be "tight."

Symptoms

Newborn infants appear healthy. Early symptoms, if present at all, are not obvious.

Symptoms may occur as mildly delayed development or failure to thrive. Increasing visual problems may lead to diagnosis of this condition.

Other symptoms include:

• Chest deformities (pectus carinatum,pectus excavatum)
• Flush across the cheeks
• High arches of the feet
• Knock-knees
• Long limbs
• Mental retardation
• Nearsightedness
• Psychiatric disorders
• Spidery fingers (arachnodactyly)
• Tall, thin build

Signs and tests

While performing a physical examination on the child, the health care provider may notice a tall, thin (Marfanoid) stature.

Other signs include:

• Curved spine (scoliosis)
• Deformity of the chest
• Dislocated lens of the eye

If there is poor or double vision, an ophthalmologist should perform a dilated eye exam to look for dislocation of the lens or nearsightedness.

There may be a history of frequent blood clots. Mental retardation, slightly low IQ, or psychiatric disease are common.

Tests:

• Amino acid screen of blood and urine
• Genetic testing
• Liver biopsy and enzyme assay
• Skeletal x-ray
• Skin biopsy with a fibroblast culture
• Standard ophthalmic exam